Immune system in mammals possesses the ability to control the homeostasis between the activation and inactivation of lymphocytes through various regulatory mechanisms during and after an immune response. Among these mechanisms, there are mechanisms that specifically modulate the immune response as and when required. Mechanism via PD-1 pathway relates to almost every aspect of immune responses including autoimmunity, tumour immunity, infectious immunity, transplantation immunity, allergy and immunological privilege. PD-1 (or Programmed Cell Death 1 or PDCD1) is a ˜55 kD type I membrane glycoprotein and is a receptor of the CD28 superfamily that negatively regulates T cell antigen receptor signalling by interacting with the specific ligands and is suggested to play significant role in the maintenance of self-tolerance.
The PD-1 protein's structure comprises of an extracellular IgV domain followed by a trans-membrane region and an intracellular tail. The intracellular tail contains two phosphorylation sites located in an immunoreceptor tyrosine-based inhibitory motif and an immunoreceptor tyrosine-based switch motif, which suggests that PD-1 negatively regulates TCR signals. Also, PD-1 is expressed on the surface of activated T cells, B cells, and macrophages, (Y. Agata et al., Int Immunol, May 1996, 8, 765) suggesting that compared to CTLA-4 [(Cytotoxic T-Lymphocyte Antigen 4), also known as CD152 (Cluster of differentiation 152), a protein that also plays an important regulatory role in the immune system], PD-1 more broadly negatively regulates immune responses.
Indeed, functional “exhaustion” (immune dysfunction) among T and B cell subsets is a well-described feature of chronic viral infections, such as hepatitis B and C and HIV viruses. T cell exhaustion was initially described for CD8 T cells in mice chronically infected with lymphocytic choriomeningitis virus clone 13. In the lymphocytic choriomeningitis virus mouse model, repeated antigen stimulation through the T cell antigen receptor drives the sustained expression of T cell inhibitory receptors, including programmed cell death-1 (PD-1) and lymphocyte activationgene-3 (LAG-3), on virus-specific CD8 T cells (Joseph Illingworth et al., Journal of Immunology (2013), 190(3), 1038-1047).
Blockade of PD-1, an inhibitory receptor expressed by T cells, can overcome immune resistance. (PD-1 is a key immune check point receptor expressed by activated T cells, and it mediates immune suppression. PD-1 functions primarily in peripheral tissues, where T cells may encounter the immune suppressive PD-1 ligands; PD-L1 (B7-H1) and PD-L2 (B7-DC), which are expressed by tumor cells, stromal cells, or both Inhibition of the interaction between PD-1 and PD-L1 can enhance T-cell responses in vitro and mediate preclinical antitumor activity (Suzanne L. Topalian et al., N Engl J. Med. 2012, 366(26): 2443-2454).
PD-1 plays critical roles in the regulation of the immune response to cancer, allergy, and chronic viral infection (Julie R. Brahmer et al., N Engl J. Med. 2012, 366(26): 2455-2465.)
Tumour cells and virus (including HCV and HIV) infected cells are known to exploit the PD-1 signalling pathway (to create Immunosuppression) in order to escape immune surveillance by host T cells. It has been reported that the PD-1 gene is one of genes responsible for autoimmune diseases like systemic lupus erythematosus (Prokunina et al., Nature Genetics, 2002, Vol. 32, No. 4, 666-669.).
Several potential immunomodulators of PD-1 have been described. For example International application WO 01/14557, WO 2004/004771, WO 2004/056875, WO 02/079499, WO 03/042402 and WO 2002/086083 report PD-1 or PD-L1 inhibitory antibody or fusion protein.
United State patent application US2011318373 reports peptide and their derivatives derived from PD1 ectodomain capable of inhibiting the programmed cell death 1 (PD1) signalling pathway.
International application number WO2011/082400 reports heteroaryl compounds and their derivatives as potential immunomodulators of PD-1. Unfortunately, there are no peptidomimetics compounds available currently as PD-1 immunomodulators.
There is a need for more potent, better and/or selective immune modulators of PD-1 pathway. In the present invention, we explore novel peptidomimetic compounds and their therapeutic usefulness as immunomodulatory agents as a new approach. Peptidomimetics compounds often mimic in the structure to peptide and the biological activity while offering the further advantages of increased oral bioavailability, bio-stability, bioefficiency, the half-life of the activity through minimizing enzymatic degradation, greater distribution within the target tissues such as tumor for improved therapeutic efficacy, higher stability at ambient temperature leading to better storage properties, lower cost of goods and easier regulatory clearance due to lack of issues related to purity such as contamination by cellular materials. The present invention therefore may provide the solution for this by offering novel synthetic peptidomimetic compounds and its derivatives which acts as immune-modulators of PD1 pathway.